Method and system for the production of a plastic needle

ABSTRACT

A method and a system is provided for producing a needle of plastic, as well as the needle of plastic which includes a needle for medical purposes. The method for producing the needle includes introducing a melt of plastic into a feed system, increasing the melt pressure gradually during melt passage through the feed system, passing the melt into the mould cavity, whereby the melt substantially fills the mould cavity, cooling the melt into the mould cavity whereby the melt solidifies to a needle, and removing the needle from the mould cavity. Increasing the pressure through the feed system provides for meeting specific pressure demands at the entrance of the mould cavity, thereby moulding thin and elongated articles.

TECHNICAL FIELD

This invention relates to a method for producing a needle of plastic, asystem for same as well as a needle of plastic, in particular a needlefor medical purposes.

PRIOR ART

Needles or cannulas for medical purposes, such as injections ofmedicine, have been produced in various sizes depending on theirintended use. For medicine to be injected frequently, such as severaltimes a day, it is preferred to use the thinnest possible needle takinginto account the viscosity of the medicine to be injected. Diabeticsinjecting insulin several times a day would preferably use a very thinneedle, such as from gauge 26 to gauge 30, in order to reduce the painas well as reduce the tissue damage resulting from each injection. Inthe present context the term “thin” refers to the diameter of the needlein question. Usually needles and other medical tubings are sized ingauges, wherein gauge 8 corresponds to 4.19 mm, and gauge 30 correspondsto 0.30 mm, for example.

In order to obtain a needle exhibiting the necessary strength forpenetrating the skin and subcutis as part of the injection the very thinneedles have usually been made from metal. Like many other medicalarticles it is of interest to produce the needles of a plastic material.

EP 452 595 discloses a method for producing a plastic medical tubing,such as a catheter, wherein a liquid crystalline polymer has beenshear-thinned to such a viscosity allowing the melt to flow into andfill a mould. The plastic tubings produced have a gauge size of from 8to 26, preferably from 14 to 20. The shear-thinning is provided bypassing the plastic melt through an orifice before the melt reaches themould. The patent describes a method for preparing the tubing byextruding the shear-thinned polymer into a mould, and describes furtherthat the polymer melt may be forced under pressure through the orificeand thence directly into the mould.

However, in order to obtain very thin needles of the length relevant forinjection of medicine very small volumes of plastic melt is used. It hasbeen found, that merely extruding the melt, optionally under pressurewill not result in the moulding of a needle of the dimensions inquestion with sufficient strength.

Injection moulding systems are often used for the production of largeamount of articles. Injection moulding is a periodical process, in whicha plastic granulate is being homogenized and melted by heating as wellas by mechanical working. The plastic melt is injected into a mouldcavity. The mould cavity has a temperature which is controlled to belower than the melting point of the plastic. Hereby the melt injectedinto the mould cavity will solidify from the wall of the mould cavity tothe centre of the article.

In the known injection moulding systems a screw may be used to themechanical working of the melt as well as to introduce the melt into themould cavity at a certain injection speed.

The screw movement or injection stroke is normally set to 1 to 4 timesof the diameter of the screw. Hereby a right quality of the melt as wellas a uniform shot volume will be ensured. By “shot volume” is meant theamount of melt necessary to at least fill the mould cavity to obtain aneedle of predetermined dimensions.

The inertia of the screw as well as the hydraulic pressure transferredto the screw ensures in the known systems a pressure which is sufficientto fill large shot volumes.

However due to the small amount of melt necessary for producing a smallarticle pressure applied to the screw cannot be timely transferred tothe melt at the entrance of the mould cavity. The matter is that thehydraulic pressure behind the screw shall build up a pressure from thescrew to the entrance of the mould cavity in approximately 1 to 10 msec,which has not been possible in known injection moulding system.Therefore, it has not previously been possible to obtain plastic needlesor cannulas for medical purposes, for which the outer diameter of theneedle or the cannula is 0.5 mm or less.

Furthermore, needles or cannulas of this diameter having an innerdiameter is very thin-walled, a wall thickness of approximately0.10-0.18 mm. This provides the problem of introducing the melt into themould cavity in such a short time, that “freezing” of the melt isavoided. By “freezing” is meant that the melt solidifies rapidly due tothe small thickness of the material. In case melt freezes in the firstpart of the mould cavity, the melt will not be able to fill the entiremould cavity and thereby a needle of predetermined dimensions will notbe obtained.

By the known methods of injection moulding it has therefore notpreviously been possible to mould needles or cannulas having a wallthickness of material of approximately 0.10-0.18 mm.

The needles or cannulas are furthermore having a very large L/D ratio(wherein L is the length, and D is the diameter of the article) whichfurther provides the problem of not only requiring a small shot volumebut also of filling the “long” mould cavity as compared to a smalldiameter. Thus, in order to ensure that the mould cavity is filledtotally with melt a very precise control of the energy reserve in themelt at the entrance of the mould cavity is necessary.

Certain requirements must be met for needles Or cannulas for medicalpurposes irrespective of the material used. One requirement is that theneedle must not bend during insertion of the needle into the patient.Many plastic needles have lacked sufficiently strength when the diameterof the needle is decreased, so that in practice it has not been possibleto use plastic needles for medical purposes unless very large needles,such as needles having a diameter of 1 mm or above.

CORE OF THE INVENTION

One aspect of the invention relates to a method for producing a plasticneedle, which needle has two ends, wherein at least the outer diameterof one end is less than 0.50 mm, said needle further having alongitudinal lumen extending between two openings of the needle, in amoulding system having an assembly comprising a feed system and a mouldcavity,

said method comprising the following steps:

introducing a melt of plastic into the feed system,

increasing the melt pressure gradually during melt passage through thefeed system,

passing the melt into the mould cavity, whereby the melt substantiallyfills the mould cavity,

cooling the melt in the mould cavity whereby the melt solidifies to aneedle, and

removing the needle from the mould cavity.

Another aspect of the invention is a system for producing a hollowplastic needle, having an assembly comprising a feed system and a mouldcavity, and further comprising means for introducing a melt of plasticinto the feed system, said feed system being arranged for increasing themelt pressure gradually during melt passage through the feed system, andmeans for passing the melt into the mould cavity, so that the meltsubstantially fills the mould cavity.

By the present invention it has been found that in order to producesmall, thin and elongated articles by injection moulding whereby theshot volume is very small it is required to ensure a high energy reservein the melt at the entrance of the mould cavity itself.

By gradually increasing the pressure through the feed system it ispossible to meet the specific pressure demands at the entrance of themould cavity in order to mould the thin and elongated articles in spiteof the small shot volume, because the melt will then reach a sufficientpressure before it enters the mould cavity.

During injection moulding the melt is in motion in the feed system, i.e.flows, whereby the flow front of the melt has a pressure ofapproximately 0.1 MPa whereas the pressure in front of the screw ishigh. Accordingly, a high pressure gradient is present.

The high pressure gradient in the feed system ensures the high energyreserve in the melt. This energy reserve in the melt has the samefunction as for example a biased spring.

When the melt is introduced into the entrance of the mould cavity theenergy reserve in the melt ensures, that the spring effect in the meltwhen released will substantially fill the mould cavity in a very shorttime. By “substantially fill” is meant that the mould cavity is filledwith melt within predetermined tolerances for needles produced.

Surprisingly, it has been found, that due to the energy reserve in themelt, the high melt pressure in front of the screw can be transferred tothe flow front of the melt in approximately 1 msec. Hereby, thesolidification or freezing of the melt before the melt actually hassubstantially filled the entire mould cavity is avoided.

Accordingly, the entire mould cavity will substantially be filled by themelt, so the predetermined length and diameter of the needles isobtained.

A third object of the invention relates to a plastic needle having twoends, said needle being produced by injection moulding from a plasticmelt, wherein the outer diameter of the moulded needle in at least oneend of the needle is less than 0.50 mm, preferably less than 0.45 mm,said needle comprising a lumen.

Hereby, a plastic needle is obtained having an outer diameter, whichdiameter is so thin that the pain as well as the tissue damage resultingfrom injections is reduced. Especially for diabetics who are injectinginsulin several times a day the thin needle is useful.

In an embodiment according to the invention the inner diameter of theneedle, e.g. the diameter of the lumen, may correspond to at most 60% ofthe outer diameter of the needle, preferably from 20% to 50% of theouter diameter. Hereby, a high strength of the needle is obtainedcompared to the size of the inner diameter.

The lumen may be formed in many different ways. In one embodimentaccording to the invention an insert in the mould cavity correspondingto the lumen of the needle may form the lumen.

In another embodiment the insert may comprise a wire substantiallycentred in the mould cavity for forming the lumen in the needle.According to the invention the wire may be fixed extending through theentire mould cavity. Hereby, the melt flows around the wire and thelumen is formed.

After the melt has solidified and the needle is formed the wire isremoved from the needle. For example, means may be arranged for removingthe wire after moulding. The removal of the wire may be carried outbefore or after the needle leaves the mould cavity.

The pressure is increased gradually through the feed system to meet thespecific pressure demands at the entrance of the mould cavity. Thepressure increase may be carried out by any suitable means.

In one embodiment the specific design of the feed system, i.e. thegeometry of the feed system, leads to an increase of the pressure.

The feed system may be comprised of a long tube having a small diameter,optionally with parts of decreasing diameter.

The diameter of the feed system may be decreased in many suitable wayssuch as stepwise or continuously. In one embodiment according to theinvention the feed system is at least partly of conical shape, or inanother embodiment the feed system comprises cylindrical parts ofdifferent diameters separated by conical parts, whereby the pressure isincreased gradually through the feed system. It is of importance toensure that a sudden increase of pressure is avoided in the feed system.

The amount of melt being introduced into the feed system shall be of arate sufficient to fill at least the feed system completely in apredetermined time interval, so the design of the feed system canincrease the pressure to a level which is enough for completely fillingthe mould cavity.

If the rate introduced is too small, the feed system will not be timelyfilled and accordingly the pressure will not be increased sufficientlyto eventually fill the mould cavity.

In cases where the rate introduced is to large, it is not possible tocontrol the increase of the pressure and thereby the complete filling ofthe mould cavity.

Therefore, the melt is preferably introduced into the feed system with arate of from 0.10 to 100 ccm/sec, preferably from 1 to 10 ccm/sec.

The feed system and mould cavity may exhibit many different temperaturesaccording to the material used in moulding process. The temperature ofthe feed system and mould cavity has a direct influence on the viscosityof the melt and thereby the ability of the melt to flow easily throughthe feed system and the mould cavity. However, the temperature may notbe to high as this will influence on the strength of the producedneedle.

According to the invention the temperature of the feed system and of themould cavity may be from 50 to 350° C., preferably from 120 to 140° C.Hereby, the flow length of the melt in the feed system and in the mouldcavity is optimal in relation to the strength of the produced needle.

In a preferred embodiment according to the invention a ring gate isarranged in front of the mould cavity, so the melt is introduced intothe ring gate before entering the mould cavity. The melt will in thisembodiment be completely confluent along the periphery of the ring gatebefore entering the mould cavity in order to avoid a burr or any othermoulding defects due to lack of confluence.

The ring gate may have many different shapes. In one embodiment the ringgate is of a conical shape. When the ring gate have an elongated conicalshape, no sudden changes in the thickness of the melt material willoccur and the melt flow will not stop.

Especially in cases where a wire is substantially centred in the ringgate and the mould cavity for forming the lumen, the melt may beintroduced radially into the ring gate. A suitable balance of the meltin the ring gate is hereby obtained. The melt will flow equally aroundthe wire and will have a uniform flow front and thereby distribution inthe mould cavity. Hereby, the produced needle avoid having a burr or anyother moulding defects.

In order to avoid that the plastic melt will freeze or solidify in themould cavity, the melt has to be introduced into the mould cavity in ashort time. According to the present invention the mould cavity may besubstantially filled in a period of time from 0.1 to 10 msec, preferablyfrom 1 to 2 msec. Hereby, the entire mould cavity will be filled withthe melt before it starts to solidify or to freeze.

The plastic needle is preferably produced from a liquid crystallinepolymer melt. The material, liquid crystalline polymer, may be used dueto the fact, that it has a high degree of molecular orientation. Duringmoulding the molecules of the liquid crystalline polymer melt arealigned substantially in the direction of the main flow of the melt.After solidification of the liquid crystalline polymer the molecularorientation is maintained. This high degree of orientation of thematerial ensures that the needles obtained exhibits high strengthcompared to needles made of other plastic materials.

The liquid crystalline polymer may be a polymer comprising monomer unitsselected from hydroxybenzoic acid, hydroxynaphtoic acid, terephtalicacid, p-aminophenol and p-biphenol alone or in combination.

In an embodiment according to the invention the polymer may be a randomcopolymer comprising 70-80% hydroxybenzoic acid and 20-30%hydroxynaphtoic acid.

The passage of the melt in the feed system ensures a gradually increasein pressure, the passage furthermore ensures that an optimal orientationof the material particles in the plastic melt is obtained. Hereby, aneedle with the necessary strength is obtained.

In order to increase the strength of the needle, the plastic melt maycomprise fibre reinforcement. The reinforcement may be selected fromglass fibre, carbon fibre, aramid fibre or any suitable fibres.

When the melt comprises fibre reinforcement the viscosity of the melt isincreased and thereby it's ability to flow is decreased. For obtaining asufficient strength of the needle in relation to the viscosity of themelt, the reinforcement fibres may constitute from 15 to 40% by weightof the solid plastic, preferably from 25 to 35%, such as approximately30%.

DETAILED DESCRIPTION

The invention will be explained more fully below with reference toparticularly preferred embodiments as well as the drawing, in which

FIG. 1 is a schematic view of an injection moulding system according tothe invention,

FIG. 2 is a schematic view of an assembly comprising the mould cavityand the feed system,

FIG. 3 is a schematic view of the mould cavity and a ring gate,

FIG. 4 is a schematic view of a first embodiment of the feed systemaccording to the invention,

FIG. 5 is a schematic view of a second embodiment of the feed systemaccording to the invention,

FIG. 6 is a sectional view of the ring gate shown in FIG. 3,

FIG. 7 is a schematic sectional view of the plastic needle.

FIG. 8 is a schematic sectional view of the vertical section A—A shownin FIG. 6, and

FIG. 9 is a view of a diagram showing the pressure as function of thetime.

All the figures are highly schematic and not necessarily to scale, andthey show only parts which are necessary in order to elucidate theinvention, other parts being omitted or merely suggested.

The moulding system 1 may be any injection moulding system suitable forinjection moulding of small articles. In FIG. 1 is shown a schematicview of a injection moulding system 1.

The system 1 comprises a granulate reservoir 2, which reservoir 2contains the plastic in a solid phase.

The granulate is at the bottom 3 of the reservoir 2 lead through a feedtube 4 into a chamber 5. In this embodiment the chamber 5 comprises ascrew 6, which screw 6 is rotated by a driving shaft 7 connected to amotor 8. An instrument for measuring pressure 9 is connected to thechamber 5 in front of the screw 6, for monitoring the pressure buildingby the screw 6. As the screw 6 rotates the granulate is led towards theentrance of an assembly 10. During the rotation of the screw 6 thegranulate is being heated and becomes a plastic melt. The temperature ismonitored by a temperature sensor 11.

The temperature of the assembly 10 is monitored by a temperature sensor12 and is controlled to be from 50 to 350° C., preferably from 120 to140° C. according to the material used in the moulding process. Hereby,the flow length of the melt in the assembly 10 is optimal in relation tothe strength of the produced needle.

The assembly 10 is shown schematic in FIG. 2. The assembly 10 comprisesin this embodiment a mould cavity 13 and a feed system 14.

The melt from the chamber 5 is introduced into the feed system 14. Fromthe feed system 14 the melt is introduced radially into the mould cavity13. In the feed system 14 the melt pressure is gradually increasedbefore the melt enters the mould cavity 13.

In the embodiment shown in FIG. 2 the pressure is increased due to thedistance the melt has to flow. The matter is that the pressure isincreased due to the flow resistance of the melt. The pressure isfurthermore increased by decreasing the diameter of the feed system 14.The feed system 14 comprises a first cylindrical part 15 having a firstdiameter and a second cylindrical part 16 having a second diameter,smaller than the first diameter. The first cylindrical part 15 isseparated from the second cylindrical part 16 by a conical part 17.

The melt pressure in this embodiment is already increased from the startof the feed system 14 and afterwards increased gradually by the passageof the melt through the feed system 14 due to the distance the melt hasto flow as well as due to the decreasing of the diameter of the feedsystem 14.

The melt pressure is increased sufficiently so the high energy reservein the melt is ensured. Hereby, the melt pressure can be transferred tothe flow front of the melt in approximately 1 msec.

In FIG. 3 is the mould cavity 13 shown separated from a ring gate 18,the function of the ring gate 18 will be explained more fully below. Themelt is in this embodiment introduced radially from the feed system 14into the ring gate 18 in respect to the melt flow in the mould cavity13. The mould cavity 13 comprises a first part 19 having a firstdiameter and a second part 20 with a second diameter smaller than thefirst diameter. The first part 19 is separated from the second part 20by a conical part 21. The diameter of the second part 20 corresponds tothe outer diameter of the needle and is less than 0.50 mm.

A wire 22 is substantially centred in the mould cavity 13 for formingthe lumen in the needle. In this embodiment the wire 22 is fixed andextends through the mould cavity 13 and further through the ring gate18. Hereby the melt flows equally around the wire during moulding andthe lumen is formed in the centre of the needle.

In FIG. 4 another embodiment of the feed system 14 according to theinvention is shown. The feed system 14 has in this embodiment a firstdiameter D_(entrance) at the entrance to the feed system 14 and a seconddiameter D_(exit) at the exit of the feed system 14. The diameter of thefeed system 14 is in this embodiment gradually decreasing along theentire length L_(feed system), so the feed system 14 exhibits a conicalgeometry.

In FIG. 5 is the feed system 14 shown in the same way as in FIG. 2. Inthis embodiment the feed system 14 is having two cylindrical partsseparated by conical parts. The first cylindrical part 15 is having adiameter corresponding to the diameter D_(entrance) at the entrance tothe feed system 14. The second cylindrical part 16 is having a diameterD_(middle), which diameter D_(middle) is smaller than the diameterD_(entrance). At the end of the feed system 14 the diameter correspondsto the diameter D_(exit), which diameter corresponds to the entrance ofthe mould cavity. The first cylindrical part 15 is separated from thesecond cylindrical part 16 by a first conical part 17. The secondcylindrical part 16 is further separated from the mould cavity by asecond conical part 23. The diameter of the feed system 14 is in thisembodiment decreased in steps along its entire length L_(feed system).

In FIG. 6 is a schematic sectional view of the ring gate 18 shown. Thearrow B indicates the main melt flow direction in the feed system. Themelt is introduced radially into the ring gate 18 (indicated by arrow B)with respect to the melt flow in the mould cavity (indicated by arrowA). A first part 24 of the ring gate 18, where the melt is introduced,is formed with a large volume around the circumference of the ring gate18, whereby the melt is forced to flow firstly along the circumferenceof the first part 24 filling the large volume with melt before enteringa second part 25 of the ring gate 18. In the second part 25 the meltflows in direction of arrow A. The second part 25 of the ring gate 18 isdesigned with an elongated conical geometry to avoid any sudden changesin geometry that otherwise could lead to melt stop.

In FIG. 7 a schematic sectional view of a plastic needle 26 is shown.The needle 26 is having a longitudinal lumen 27 extending between oneopening 28 at a first end 29 of the needle 26 and a second opening 30 ata second end 31.

FIG. 8 shows a sectional view of the vertical section A—A of the needle26. In this embodiment the needle 26 is round and has an outer diameterD_(needle) as well as an inner diameter D_(lumen).

A plastic needle being produced according to the invention having anouter diameter of 0.40 mm and a length of 8.00 mm. The needle is furtherhaving a lumen with a diameter of 0.16 mm. The wall of the needle is inthis embodiment 0.12 mm.

The plastic melt used is a liquid crystalline polymer, which is a randomcopolymer comprising 73% hydroxybenzoic acid and 27% hydroxynaphtoicacid.

The needle is being produced in an injecting moulding system having anassembly comprising a feed system, a ring gate as well as a mouldcavity.

The screw used in the injecting moulding system has a 15 mm screw. Theinjection moulding system is set to introduce approximately 2.6 ccm ofmelt into the feed system with an injection speed of 3 ccm/sec. Thetemperature of the assembly is controlled to 130-140° C.

The geometrical form of the feed system is as follows, an entrancediameter of 4.00 mm, a first cylindrical part with a diameter of 2.50 mmfor distance of 449.00 mm, a second cylindrical part with a diameter on1.60 mm for a distance of 10.00 mm, separated by a conical part for adistance of 10.00 mm.

The diagram in FIG. 9 shows an abscissa and an ordinate. At the abscissathe time is indicated as seconds, and at the ordinate the pressure isindicated as MPa. The diagram shows the melt pressure at the entrance tothe feed system as function of the time during filling of the assembly.In the diagram it is shown, that the pressure is being increasedgradually for about a second during the melts passage of the feedsystem. At about 1 sec on the abscissa, the pressure have a highincrease due to the small diameter of the mould cavity. The highpressure in the melt will due to the energy reserve be transferred tothe flow front of the melt, so the entire mould cavity will be filledbefore the melt starts to solidify.

Hereby, the pressure of the melt will be increased during passage of thefeed system, so the energy reserve in the melt will be sufficient tofill the entire mould cavity in approximately 1 msec. Accordingly, theproduced needle will obtain the predetermined size as mentioned before.

What is claimed is:
 1. A method for producing a plastic needle, whichneedle has two ends, wherein at least the outer diameter of one end isless than 0.50 mm, said needle further having a longitudinal lumenextending between two openings of the needle, in a moulding systemhaving an assembly comprising a feed system and a mould cavity, whereinan insert is corresponding to the lumen of the needle for forming thelumen in the needle, said method comprising the following steps:introducing a melt of plastic into the feed system, increasing the meltpressure gradually during melt passage through the feed system, passingthe melt into the mould cavity whereby the melt solidifies to a needle,the mould cavity being substantially filled in a period of time from 0.1to 10 msec, and removing the needle from the mould cavity.
 2. The methodaccording to claim 1, wherein the melt is introduced into the feedsystem with a rate of from 0.10 to 100 ccm/sec.
 3. The method accordingto claim 1, wherein the mould temperature is from 50 to 350° C.
 4. Themethod of claim 2, wherein the rate is from 1 to 10 ccm/sec.
 5. Themethod of claim 3, wherein the mould temperature is from 120 to 140° C.6. A method for producing a plastic needle, which needle has two ends,wherein at least the outer diameter of one end is less than 0.50 mm,said needle further having a longitudinal lumen extending between twoopenings of the needle, in a moulding system having an assemblycomprising a feed system and a mould cavity, wherein an insert iscorresponding to the lumen of the needle for forming the lumen in theneedle, said method comprising the following steps: introducing a meltof plastic into the feed system, increasing the melt pressure graduallyduring melt passage through the feed system, passing the melt into themould cavity whereby the melt solidifies to a needle, the mould cavitybeing substantially filled in a period of time from 1 to 2 msec, andremoving the needle from the mould cavity.